Evolution of Tight-Gas Fracturing Methodology in the Lower Paleozoic Sandstone Formations of Saudi Arabia

摘要

The lower Paleozoic Sandstone Formations in Saudi Arabia range from as deep as 20,000 ft in the South Ghawar and Rub’Al- Khali to less than 12,000 ft in the northwest. The deeper, tight-gas projects in the South Ghawar and Rub’Al-Khali have seen the highest activity since 2006. They are the subject of this review in light of four key wells. The targeted lower Paleozoic formations in these wells are Sarah, Qasim, and the Rhuddannian sandstones in the Qusaiba formation. The Sarah and Qasim formations are sandstones while the Qusaiba is interbedded sandstone and shale. The high pressure, high temperature (HPHT) environment in these reservoirs poses serious technical challenges that must be overcome when hydraulic fracture stimulation is attempted. Specific challenges to fracture treatment design in these deep, lower Paleozoic intervals include proppant selection, interaction of fracturing fluid with the formation, interaction of fracturing fluid with drilling mud, fracturing fluid clean-up and load recovery. The four key wells show an evolution in the design methodology to meet these technical challenges. The evolutionary steps take into account geological, geomechanical, and petrophysical analyses that are calibrated with field data as the project matured. The accompanying lab work has also led to permeability profiles, well-calibrated stress regimes, and, overall, an enhanced understanding of these complex reservoirs. In turn, better reservoir understanding has improved the completion strategy. The four key wells provide a detailed account and up-to-date documentation of the experiences gained in the last four years. Early on, a fluid selection strategy was developed based on the fracture gradient. As field data became available, geomechanics studies determined that fracture confinement was the result of a change in the stress regime. Finally, the need for multistage fracturing was established to optimize production. The lessons learned from these experiences have guided future exploration activities in the area.